Indifferent electrode pad systems and methods for tissue ablation

ABSTRACT

Systems and methods for transmitting energy through patient tissue involve the use of an indifferent pad assembly in conjunction with an ablation probe. Systems may include an electrical surgical unit having a power output connector, a first power return connector, and a second power return connector. Systems may also include an ablation probe coupleable with the power output connector of the electrical surgical unit, and an indifferent pad assembly having a conductive mechanism coupled with an electrical and thermal insulator mechanism, and a wire assembly coupled with the conductive mechanism. The wire assembly can include a first connector coupleable with the first power return connector of the electrical surgical unit, and a second connector coupleable with the second power return connector of the electrical surgical unit.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a nonprovisional of, and claims the benefit of priority to, U.S. Provisional Patent Application No. 61/318,474 filed Mar. 29, 2010 (docket no. 87512-784699; previously 021063-003500US). This application is also related to U.S. patent application Ser. No. ______ filed Mar. 29, 2011 (docket no. 87512-798150; previously 021063-004100US) and U.S. Pat. No. 7,288,090, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Embodiments of the present invention related to medical devices and methods, and in particular to cardiac ablation systems and methods.

Atrial fibrillation (AF) is a common clinical condition, and presents a substantial medical issue to aging populations. AF is costly to health systems, and can cause complications such as thrombo-embolism, heart failure, electrical and structural remodeling of the heart, and even death.

For many years, the main treatment for atrial fibrillation (AF) involved pharmacological intervention. More recently, the focus has shifted toward surgical or catheter ablation options to treat or effect a cure for AF. The ablation techniques for producing lines of electrical isolation are now replacing the so-called Maze procedure. The Maze procedure uses a set of transmural surgical incisions on the atria to create fibrous scars in a prescribed pattern. This procedure was found to be highly efficacious but was associated with a high morbidly rate. The more recent approach of making lines of scar tissue with modern ablation technology has enabled the electrophysiologist or cardiac surgeon to create the lines of scar tissue more safely. Ideally, re-entrant circuits that perpetuate AF can be interrupted by the connected lines of scar tissue, and the goal of achieving normal sinus rhythm in the heart may be achieved.

Triggers for intermittent AF and drivers for permanent AF can be located at various places on the heart, such as the atria. For example, where triggers or drivers are located near the pulmonary veins, it follows that treatment may involve electrical isolation of the pulmonary veins.

Certain cardiac surgical procedures involve administering ablative energy to the cardiac tissue in an attempt to create a transmural lesion on the tissue. However, some monopolar approaches may present a risk of injury or damage to tissue located near the treatment site. Relatedly, some current bipolar approaches may be limited due to structural constraints associated with the use of a clamping device. For example, although bipolar radiofrequency can be a reliable way to create transmural atrial scars, the clamping design of bipolar devices can limit its use in certain anatomical applications. Hence, there continues to be a need for improved systems and methods that can safely and effectively deliver ablative energy to patient tissue in a uniform and reproducible manner.

Although current and proposed treatments may provide real benefits to patients in need thereof, still further advances would be desirable. For example, it would be desirable to provide improved systems and methods for delivering ablation treatment while reducing the risk of damage to tissue surrounding the treatment site. Embodiments of the present invention provide solutions that address the problems described above, and hence provide answers to at least some of these outstanding needs.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention encompass ablation systems and methods involving the use of a flexible indifferent electrode pad assembly. In some cases, the indifferent electrode pad assembly is shaped to fit in the pericardial space and conform to the posterior portion of the left atrium and right atrium. The pad assembly can include a conductive surface on the side of the pad that faces the atria, in combination with an electrical and thermal insulator. Relatedly, the pad can provide a return path in the pericardial space. The conductive surface can be electrically coupled with a thin flexible cable that connects to an Electrical Surgical Unit (ESU) to return current originating from a separate ablation device or probe. The pad assembly can operate to prevent or inhibit potential damage to the esophagus and to other non-cardiac tissues or devices, for example by isolating those tissues or preventing transmitted ablation energy from reaching them. The pad assembly, used in combination with an endocardial surgical ablation monopolar probe, can also enhance the effect of the ablation because current spread can be less than would otherwise occur when a monopolar probe is used in conjunction with a return electrode placed on the patient's skin. For lesions applied near the posterior aspect of the atria, system embodiments can produce lesions similar to those made by bipolar clamping devices, while maintaining the benefit of easy application of all ablation lines used for a modified MAZE procedure. Hence, embodiments of the present invention provide an efficient and safe ablation treatment, without the geometric constraints or limitations associated with some bipolar treatments, and without the risk of complication sometimes associated with other monopolar treatments.

In an exemplary approach, an indifferent pad assembly may be used in conjunction with a monopolar probe or wand device such as the COBRA® Surgical Probe (Estech, San Ramon, Calif.), a malleable epicardial or endocardial probe that utilizes multiple electrodes to create uniform, reproducible linear lesions. This combination enables the flexibility and ease of use of monopolar ablation and the efficacy of the bipolar clamping devices. Relatedly, combination indifferent pad assembly and monopolar probe systems can be used to safely treat patient tissue with reduced risk to surrounding tissue. For example, the pad assembly and probe can be used to treat atrial tissue, without a high risk of damage to non-cardiac tissue such as the esophagus, lung, and the like.

In one aspect, embodiments of the present invention encompass methods of transmitting energy through a left atrial wall tissue of a patient. Exemplary methods may include positioning an indifferent pad assembly within the patient's pericardial space, so that a conductive mechanism of the pad assembly faces toward an external side of the left atrial wall tissue, and an insulative mechanism of the pad assembly faces toward the patient's esophagus. The pad assembly may include a return line or wire that is coupled with or in electrical connectivity with the conductive mechanism. Methods may also include advancing an ablation probe of an positioning an electrophysiological device through an opening in the patient's left atrium, positioning the ablation probe within the left atrium at an internal side of the left atrial wall tissue, so that the left atrial wall tissue is disposed between the ablation probe and the conductive mechanism of the pad assembly, and transmitting energy from the ablation probe of the electrophysiological device through the left atrial wall tissue and to the conductive mechanism of the pad assembly, while shielding the esophagus with the insulative mechanism of the pad assembly. Exemplary techniques may include returning energy from the conductive mechanism of the pad assembly to an electrosurgical unit via the return line. In some cases, the step of transmitting energy includes transmitting RF energy from the ablation probe of the electrophysiological device through the left atrial wall tissue and to the conductive mechanism of the pad assembly. In some cases, the step of transmitting energy through the left atrial wall tissue creates a lesion in the left atrial wall tissue. Optionally, the step of transmitting energy through the left atrial wall tissue may create a lesion in a posterior aspect of the left atrial wall tissue.

In another aspect, embodiments of the present invention encompass systems for transmitting energy through a tissue of a patient. Exemplary systems may include an electrical surgical unit having a power output connector, a first power return connector, and a second power return connector. Systems may also include an ablation probe coupleable with the power output connector of the electrical surgical unit. Further, systems may include an indifferent pad assembly having a conductive mechanism coupled with an electrical and thermal insulator mechanism, and a wire assembly coupled with the conductive mechanism. The wire assembly can have a first connector coupleable with the first power return connector of the electrical surgical unit, and a second connector coupleable with the second power return connector of the electrical surgical unit. In some cases, the conductive mechanism and the electrical and thermal insulator mechanism can be configured for placement between the pulmonary veins of the patient. In some cases, the electrical surgical unit can be configured to sense current individually through the first and second power return connectors, and to shut off power if current to either return connector exceeds a predetermined amount of current. Optionally, the predetermined amount of current can be one ampere.

For a fuller understanding of the nature and advantages of the present invention, reference should be had to the ensuing detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-4 illustrate aspects of ablation treatment systems and methods according to embodiments of the present invention.

FIG. 5 is a front elevation view of an electrosurgical unit in accordance with embodiments of the present invention.

FIG. 6 shows an indifferent pad assembly according to embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention encompass indifferent electrode pad systems and methods for performing endocardial ablation in a patient in need thereof. For example, such techniques are well suited for treating patients who present with atrial fibrillation and other electrical abnormalities of the heart such as incessant ventricular tachycardia. Cardiac conditions such as these can lead to thrombo-embolisms, heart failure, and other complications in a patient. These treatment approaches provided herein can result in electrical isolation or blockage between various portions of cardiac tissue, optionally via the creation of transmural ablations at selected locations on the endocardium. For example, methods and systems can be used to create scars that produce lines of electrical isolation, so as to inhibit or prevent electrical activity which may otherwise lead to or perpetuate atrial fibrillation, or so as to promote or maintain normal sinus rhythm in the patient. In some cases, these techniques can be used to form lesions at or near the pulmonary veins, the left atrial appendage, or the mitral valve, for example. Techniques can be used to treat patients presenting with paroxysmal or intermittent atrial fibrillation, as well as persistent or long lasting persistent atrial fibrillation.

Soft tissue coagulation that is performed using electrodes to transmit energy to tissue, whether catheter-based or surgical probe-based, may be performed in both bi-polar and uni-polar modes. In the uni-polar mode, energy emitted by the electrodes supported on the catheter or surgical probe is returned through one or more indifferent electrodes. In some cases, a uni-polar mode is useful because the uni-polar mode allows for individual electrode control.

Embodiments of the present invention provide techniques for applying endocardial lesions to tissue at or near the pulmonary vein (PV) ostia and other locations of the heart, to cause or enhance conduction block at the junction of the PV and left atrium as well as other blocking lesions. Such techniques are well suited for use with patients presenting with paroxysmal (focal) atrial fibrillation. Exemplary embodiments involve the administration of precisely controlled ablative energy, or controlled power, to create reproducible, uniform transmural lesions during cardiac surgery. Such techniques enable rapid and effective ablative lesions in a variety of clinical situations, including endocardial and epicardial ablations. By forming the transmural ablations, surgeons are able to achieve conduction block in the patient. Advantageously, embodiments of the present invention can be used to create complete lesion sets and reliably produce transmural lesions on a beating heart. According to embodiments disclosed herein, transmural lesions across the atrial wall can be performed reliably and efficiently. Relatedly, although many of the examples described herein are with reference to ablation of cardiac tissue such as the left atrial wall, embodiments of the present invention encompass systems and methods for ablating other tissues in the body, such as the tissue wall of various hollow organs.

Embodiments also includes ablation systems having an ablation energy source for providing energy to the ablation device. An ablation energy source is typically suited for use with ablation apparatus as described herein using RF energy. With regard to RF ablation, a typical RF ablation system includes a RF generator which feeds current to an ablation device, including those described in this application, containing a conductive electrode for contacting targeted tissue. The electrical circuit can be completed by a return path to the RF generator, provided through the patient and a large conductive plate, which is typically in contact with the patient's back. Embodiments encompass ablation using RF electrodes, including single RF ablation electrodes. Although ablation energy is often described herein in terms of RF energy, it is understood that embodiments are not limited to such ablation modalities, and other kinds of ablation energy sources and ablation devices may be used. Hence, with regard to the ablation techniques disclosed herein, other suitable ablation elements or mechanisms, instead or in addition to an RF electrode, can be used. Embodiments of the present invention therefore encompass any of a variety of ablation techniques, including without limitation irreversible electroporation, infrared lasers, high intensity focused ultrasound (HIFU), microwave, Cryoablation (killing or damaging the tissue by freezing), radiation, and the like. In some cases, an ablation mechanism can include an ablation element that transmits or delivers RF energy to patient tissue. Optionally, suitable ablation elements can transmit or deliver high voltage pulses, infrared laser energy, high intensity focused ultrasound (HIFU) energy, microwave energy, Cryoablation energy, radiation energy, and the like. Embodiments encompass ablation mechanisms having multiple ablation elements, such as multiple RF electrodes. According to some embodiments, an ablation element may include a monopolar electrode. Any of these modalities is well suited for use in endocardial ablation techniques resulting in electrical isolation and transmurality.

Turning now to the drawings, FIG. 1 illustrates aspects of ablation treatment systems and methods according to embodiments of the present invention. FIG. 1 illustrates a posterior view of the heart, as viewed through the rear ribs or backbone. As shown here, a pad assembly 100 can be positioned anterior to the esophagus and posterior to the heart. An exemplary pad assembly 100 may include a conductive mechanism or surface 110 on the side of the pad assembly that faces toward the atria, an electrical and thermal insulator mechanism 120 on the side of the pad assembly that faces toward the esophagus, and an electrical wire assembly 130 that provides electrical connectivity between the conductive mechanism 110 and an Electrical Surgical Unit (ESU). A portion of the pad is disposed central to the four pulmonary veins (PV's). For example, in some cases, the pad spans or covers at least about 80% of the area between the right and left pulmonary veins. It is understood that the pulmonary veins, esophagus, pericardium, skeleton, and other anatomical features may not be rigidly attached with one another, the heart may move relative to the esophagus due to a variety of factors, including gravity, patient swallowing, or other movement of the patient during surgery. Hence, the pad can be configured to cover a selected amount of space between the pulmonary veins, to accommodate for the shifting of such anatomical features while still providing protection to the esophagus or other tissue during an ablation treatment.

Pad assemblies may be used in concomitant cardiac surgery cases, for example in patients undergoing mitral valve repair or replacement, aortic valve replacement, and/or coronary artery bypass grafting (CABG) surgery concomitant with ablative therapy. Such treatments can involve creating a medial stenotomy or large incision splitting the breastbone, and placing the pad assembly within the pericardial space. In some cases, the surgeon may prepare a pericardial cradle, splitting the pericardium, and suspending the split or cut edges to provide a sling that supports or holds the heart. The pad assembly can be placed to the left of heart, slipped around a region proximal to left atrial appendage, and directed into position between the two sets of pulmonary veins. In some instances, the pad assembly can be advanced from the apical side of heart, pushed toward the base, guided behind the heart, and moved slightly toward the surgeon, thus disposing the pad assembly between the right and left pulmonary veins, such that the pad assembly terminates or is placed against the pericardial reflection. In some cases, the pad assembly may contact the left ventricle, and may be supported or at least partially held in place by the left ventricle. In some cases, a lower tail 150 of the pad assembly can help to provide mechanical stability when the pad assembly is positioned within the patient's body.

Treatment systems which include a pad assembly and ablation probe may be used to create lesions in any of a variety of tissues, including atrium or ventricle tissue, on either of the right or left sides. The pad assembly can operate to physically or geometrically constrain the application of the ablation by the probe. In some cases, patients presenting certain diseases may have larger or smaller than normal heart dimensions. For example, a particular patient may have a left atrium that is larger than normal. Hence, pad assemblies can be configured in a variety of shapes and sizes for use suitable with a particular patient. Typically, the pad assembly has a size and shape that covers a certain percentage of the posterior atrial surface. In some cases, the pad assembly can have a size and shape that covers about 80% or more of the tissue area located between the pulmonary veins.

FIG. 2 illustrates a top view of a transverse section of a patient 201. As shown here, a pad assembly 200 can be positioned anterior to the esophagus and posterior to the heart, for example in the pericardial space. FIG. 2 also depicts an ablation probe 205 disposed within an interior chamber of the heart. Indifferent electrode pad assembly 200 provides a return path in the pericardial space. Pad assembly 200 can be shaped to fit in the pericardial space and conform to the posterior portion of the left atrium and right atrium. Pad assembly 200 can include a conductive surface on the side of the pad assembly that faces toward the atria, and an electrical and thermal insulator mechanism 220 on the side of the pad assembly that faces toward the esophagus. Conductive surface or mechanism 210 can be electrically coupled with a thin flexible cable 230 that connects to an Electrical Surgical Unit (ESU) 240 to return current originating from a separate ablation device or probe. Pad assembly 200 can operate to prevent or inhibit potential damage to the esophagus and to other non-cardiac tissue.

Conductive mechanism or surface 210 can include a flexible conductor material, and electrical and thermal insulator mechanism 220 can include a foam or other material which prevents or inhibits the flow or transfer of heat or electricity. The electrical insulating properties can help prevent or inhibit heating when current is passed through the assembly. The thermal insulating properties can help prevent or inhibit thermal transfer which may cause tissue char. The conductive material can have a thickness within a range from about 0.002 to about 0.008 inches. In some cases, the thickness of the conductive material is about 0.005 inches. The conductive material may include any of a variety of conductive components, such as stainless steel, nickel coated copper, platinum, gold, or any other nontoxic conductive materials. The structure of the surface conductor can be a mesh, film, or the like. The insulating material can have a thickness within a range from about 0.5 mm to about 1.5 mm. In some cases, the thickness of the conductive material is about 1 mm. The insulating material may include any of a variety of insulating components, such as polyurethane foam or the like.

Pad assembly 200, used in combination with an endocardial surgical ablation probe such as probe 205, can also enhance the effect of the ablation because current will not spread as much as current would otherwise spread in the situation where a return electrode is placed on the patient's skin. An ESU can be configured to provide power control using standard power delivery algorithms. Typically, the ESU is configured to operate in a stable matter during ablation procedures involving any of a variety of tissue types having different degrees of thermal capacity.

In some instances, conductive mechanism or surface 210 can be coated with a conductive coating, such as a conductive hydrogel. Such hydrogels can be configured to provide about 500 ohm-cm resistivity. Optionally, the resistivity of the hydrogel can be configured to match the resistivity of the tissue which it contacts. In this way, electrical discontinuity between the pad assembly and the tissue surface is reduced or minimized, to reduce edge currents, i.e. the very high current densities (and high heating) that would otherwise occur at the edge of the electrical pad assembly.

An exemplary surgical procedure may include opening the pericardium, inserting the pad assembly 200 along the posterior aspect of the left ventricle, and advancing the pad assembly adjacent the right coronary to position the pad assembly posterior to the heart, for example posterior to the left atrial appendage.

A surgeon may use a pad assembly and ablation provide during a treatment procedure in which the left atrium is open. For example, a cardiopulmonary bypass technique can be used to remove blood from the heart, and an ablation probe device 205, which may include a monopolar probe, can be inserted within the heart chamber. Optionally, the surgeon may use a visualization device as an aid in positioning the ablation probe or pad assembly. In some cases, the surgeon may view or evaluate the heart tissue curvature or contour, and bend or form the ablation electrode device to provide a corresponding curvature or contour in the device. The surgeon may then contact the atrial wall or tissue with the formed device. According to some embodiments, the pad assembly is placed within the pericardial space, between the pericardium and the heart, and ablations are performed in the left atrium. During the ablation procedure, the ablation probe can be moved and positioned within the heart chamber and relative to the pad assembly, as desired. Hence, the pad assembly can be placed near the posterior part of atrium, and the probe device can be moved independent of the pad assembly. In this way, the surgeon is free to create lesions at any of a variety of locations, such as at or near the mitral valve annulus, which may otherwise be difficult using some known bipolar clamping devices.

Typically, a pad assembly conductive mechanism is much more conductive than the patient tissue, and behaves like an isopotential surface. When the ablation probe electrode is positioned directly across from the pad assembly, the ablation probe device and return pad assembly combination can operate in a fashion similar to that of a bipolar ablation system, with current remaining within a constrained region, passing from the ablation probe, directly through the tissue, and to the pad assembly. When the ablation probe electrode and pad assembly are positioned at a further distance from one another, the ablation probe device and return pad assembly combination can operate in a fashion similar to that of a monopolar ablation system, where the current traveling from the ablation probe and spreading out in all directions, with current density (and heating rate) decreasing rapidly as a function of distance from the ablation probe. Put another way, as the distance between the ablation electrode and the pad assembly becomes greater, there is a corresponding transition from a bipolar lesioning configuration to a monopolar lesioning configuration. Relatedly, the heat generated is proportional to the square of the current. Hence, if a current is distributed in a way to provide 10% of an original amount of current, the resulting rate of heat generation will be about 1% of original rate of heating. As noted elsewhere herein, the indifferent pad assembly can operate to prevent or inhibit noncardiac tissue, such as the esophagus, from being damaged during an ablation procedure.

In some cases, tissue positioned between the pad assembly and the ablation electrode may provide minimal or nominal resistance. For example, a tissue such as the atrial wall may provide about 10 ohms of resistance. Relatedly, certain ESU devices may not operate effectively in low resistance circumstances. For example, ESU devices may not operate as desired when the resistance is less than about 25 ohms. With continued reference to FIG. 2, in some embodiments pad assembly 200 may include one or more noninductive power resistors 260 in operative association with the return lines. As shown here, the pad assembly can include two return lines 230, and each of these lines may include two noninductive power resistors 260. Each of the resistors may provide, for example, between about 10 and about 50 ohms of resistance. In some cases, the pad assembly 200 is configured to allow up to 2 amps of current equally distributed in each of two return lines.

An ESU can be configured to monitor return current separately from two return paths. If the current exceeds a predetermined threshold, the ESU may be configured to automatically reduce or terminate power delivery.

FIG. 3 illustrates an anterior view of the heart, as viewed through the front ribs or sternum. As shown here, a monopolar probe assembly 310 can be placed within an interior chamber of the heart, and a pad assembly can be placed posterior to the heart. A pericardial reflection is typically present between the right and left pulmonary veins. The process of ablating between the right and left pulmonary veins, for example as illustrated by lesion or ablation pattern, may involve a concomitant dissection of the pericardial reflection between the right and left pulmonary veins at or near the epicardium. The pericardial reflection presents a ridge or line of attachment between the right and left pulmonary veins. For example, FIG. 3 illustrates a pericardial reflection between the right pericardial veins and the left pericardial veins. Embodiments of the present invention provide systems and methods for performing any of a variety of lesions or lesion sets on heart tissue. For example, embodiments encompass the performance of a posterior left atrial connection (PLAC) between 2 PV-encircling ablations epicardially. Embodiments may also encompass the performance of left atrial ablations. Embodiments also encompass the creation of any of the lesions sets described in U.S. patent application Ser. Nos. 12/124,743 and 12/124,766 filed May 21, 2008, the disclosures of which are incorporated herein by reference.

FIG. 4 illustrates aspects of ablation treatment systems and methods according to embodiments of the present invention. Specifically, FIG. 4 depicts a posterior view of the heart, as viewed through the rear ribs or backbone. As shown here, a pad assembly 400 can be positioned anterior to the esophagus and posterior to the heart. An exemplary pad assembly 400 may include a conductive mechanism or surface 410 on the side of the pad assembly that faces toward the atria, an electrical and thermal insulator mechanism 420 on the side of the pad assembly that faces toward the esophagus, and an electrical wire assembly 430 that provides electrical connectivity between the conductive mechanism 410 and an Electrical Surgical Unit (ESU). A portion of the pad is disposed central to the four pulmonary veins (PV's). For example, in some cases, the pad spans or covers at least about 80% of the area between the right and left pulmonary veins. It is understood that the pulmonary veins, esophagus, pericardium, skeleton, and other anatomical features may not be rigidly attached with one another, the heart may move relative to the esophagus due to a variety of factors, including gravity, patient swallowing, or other movement of the patient during surgery. Hence, the pad can be configured to cover a selected amount of space between the pulmonary veins, to accommodate for the shifting of such anatomical features while still providing protection to the esophagus or other tissue during an ablation treatment.

Indifferent pad assemblies can be used in conjunction with an electrosurgical unit (ESU) such as the ESU 500 shown in FIG. 5. ESU 500 can be used to supply and control power to a surgical probe or other electrophysiological device, and may include a plurality of displays 522, as well as buttons 524, 526 and 528 that are respectively used to control which of the electrodes on the electrophysiological device receive power, the level of power supplied to the electrodes, and the temperature at the electrodes. Power is supplied to the surgical probe or other electrophysiological device by way of a power output connector 530. Lesion creation procedures sometimes require that up to 2 amperes be returned to the ESU 500 and, to that end, an indifferent pad assembly that can handle up to 2 amperes can be placed within the patient's body and connected with the ESU. The indifferent pad assembly electrodes can be connected to a pair of power return connectors 532 and 534 on the ESU 500. The power return connectors 532 and 534 in the exemplary ESU 500 illustrated in FIG. 5 has a rectangular profile and recessed male pins 536, while the power output connector 530 has a circular profile. In order to mate with the rectangular power return connectors 532 and 534, the connector 160 (shown in FIG. 1) of the pad assembly includes a mating portion 162 with a rectangular profile and longitudinally extending female pin-connects 164. The profile need not be perfectly rectangular so long as the profile substantially corresponds to that of the power return connectors 532 and 534. For example, the middle of the top and bottom surfaces of mating portion 168 may include longitudinally extending grooves for mechanical keying with the corresponding connector. The shape and style of the power return connectors 532 and 534 and the corresponding mating portion 162 on the connector 160 need not be rectangular. However, in many cases, both will have the same general shape and this shape will be different than the shape of the power output connector 530, which need not be circular, to prevent users from attempting to plug an indifferent pad assembly into a power output connector and/or an electrophysiological device into a power return connector. Alternatively, the power output power return connectors could have the same general shape and noticeably different sizes to prevent confusion. Color coding may also be used.

FIG. 6 illustrates aspects of an indifferent pad assembly 600 according to embodiments of the present invention. Pad assembly 600 may include a conductive mechanism or surface 610 on the side of the pad assembly that faces toward the atria, an electrical and thermal insulator mechanism 620 on the side of the pad assembly that faces toward the esophagus, and an electrical wire assembly 630 that provides electrical connectivity between the conductive mechanism 610 and an Electrical Surgical Unit (ESU). Conductive mechanism or surface 610 can include a flexible conductor material, and electrical and thermal insulator mechanism 620 can include a foam or other material which prevents or inhibits the flow or transfer of heat or electricity. As shown here, wire assembly 630 may include a cable 632 having two wire mechanisms 634 and 636 extending from the pad or conductive mechanism 620. The cable splits at a “Y”, and two separated cable sections 644 and 646 terminate at connectors 650 and 660, respectively, which in turn may be connected with, for example, power return connectors 532 and 534, respectively, of the ESU shown in FIG. 5. The ESU can be configured to sense current individually to each connection and shut off power if current to either return connection exceeds a predetermined amount, for example 1 ampere. As described elsewhere herein, in some situations for the pad assembly, ablation will occur at the return indifferent pad assembly, which can correspond to a bipolar mode technique.

In some cases, embodiments of the present invention can incorporate various aspects of treatment systems and methods which are disclosed in previously incorporated U.S. patent application Ser. No. ______ filed Mar. 29, 2011 (docket no. 87512-798150).

Individual system elements or aspects of a tissue treatment computer system may be implemented in a separated or more integrated manner. In some embodiments treatment systems, which may include computer systems, which may be part of or operatively associated with an electrosurgical unit (ESU) such as the ESU 500 shown in FIG. 5, also include software elements, for example located within a working memory of a memory, including an operating system and other code, such as a program designed to implement method embodiments of the present invention. In some cases, software modules implementing the functionality of the methods as described herein, may be stored in a storage subsystem. It is appreciated that systems can be configured to carry out various method aspects described herein. Each of the devices or modules of the present invention can include software modules on a computer readable medium that is processed by a processor, hardware modules, or any combination thereof. Any of a variety of commonly used platforms, such as Windows, MacIntosh, and Unix, along with any of a variety of commonly used programming languages, such as C or C++, may be used to implement embodiments of the present invention. In some cases, tissue treatment systems include FDA validated operating systems or software/hardware modules suitable for use in medical devices. Tissue treatment systems can also include multiple operating systems. For example, a tissue treatment system can include a FDA validated operating system for safety critical operations performed by the treatment system, such as data input, power control, diagnostic procedures, recording, decision making, and the like. A tissue treatment system can also include a non-validated operating system for less critical operations. In some embodiments, a computer system can be in integrated into a tissue treatment system, and in some embodiments, a computer system can be separate from, but in connectivity with, a tissue treatment system. It will be apparent to those skilled in the art that substantial variations may be used in accordance with any specific requirements. For example, customized hardware might also be used and/or particular elements might be implemented in hardware, software (including portable software, such as applets), or both. Further, connection to other computing devices such as network input/output devices may be employed. Relatedly, any of the hardware and software components discussed herein can be integrated with or configured to interface with other medical treatment or information systems used at other locations.

While the exemplary embodiments have been described in some detail, by way of example and for clarity of understanding, those of skill in the art will recognize that a variety of modification, adaptations, and changes may be employed. Hence, the scope of the present invention should be limited solely by the claims. 

1. A method of transmitting energy through a left atrial wall tissue of a patient, the method comprising the steps of: positioning an indifferent pad assembly within the patient's pericardial space, so that a conductive mechanism of the pad assembly faces toward an external side of the left atrial wall tissue, an insulative mechanism of the pad assembly faces toward the patient's esophagus, and a return line of the pad assembly is coupled with the conductive mechanism; advancing an ablation probe of an electrophysiological device through an opening in the patient's left atrium; positioning the ablation probe within the left atrium at an internal side of the left atrial wall tissue, so that the left atrial wall tissue is disposed between the ablation probe and the conductive mechanism of the pad assembly; transmitting energy from the ablation probe of the electrophysiological device through the left atrial wall tissue and to the conductive mechanism of the pad assembly, while shielding the esophagus with the insulative mechanism of the pad assembly; and returning energy from the conductive mechanism of the pad assembly to an electrosurgical unit via the return line.
 2. The method according to claim 1, wherein the step of transmitting energy comprises transmitting RF energy from the ablation probe of the electrophysiological device through the left atrial wall tissue and to the conductive mechanism of the pad assembly.
 3. The method according to claim 1, wherein the step of transmitting energy through the left atrial wall tissue creates a lesion in the left atrial wall tissue.
 4. The method according to claim 1, wherein the step of transmitting energy through the left atrial wall tissue creates a lesion in a posterior aspect of the left atrial wall tissue.
 5. A system for transmitting energy through a tissue of a patient, the system comprising: an electrical surgical unit having a power output connector, a first power return connector, and a second power return connector; an ablation probe coupleable with the power output connector of the electrical surgical unit; and an indifferent pad assembly comprising a conductive mechanism coupled with an electrical and thermal insulator mechanism, and a wire assembly coupled with the conductive mechanism, wherein the wire assembly comprises a first connector coupleable with the first power return connector of the electrical surgical unit, and a second connector coupleable with the second power return connector of the electrical surgical unit.
 6. The system according to claim 5, wherein the conductive mechanism and the electrical and thermal insulator mechanism are configured for placement between the pulmonary veins of the patient.
 7. The system according to claim 5, wherein the electrical surgical unit is configured to sense current individually through the first and second power return connectors, and to shut off power if current to either return connector exceeds a predetermined amount of current.
 8. The system according to claim 7, wherein the predetermined amount of current comprises one ampere.
 9. A method of transmitting energy through a left atrial wall tissue of a patient, the method comprising the steps of: positioning an indifferent pad assembly within the patient's pericardial space, so that a conductive mechanism of the pad assembly faces toward an external side of the left atrial wall tissue, and an insulative mechanism of the pad assembly faces toward the patient's esophagus; advancing an ablation probe of an electrophysiological device through an opening in the patient's left atrium; positioning the ablation probe within the left atrium at an internal side of the left atrial wall tissue, so that the left atrial wall tissue is disposed between the ablation probe and the conductive mechanism of the pad assembly; and transmitting energy from the ablation probe of the electrophysiological device through the left atrial wall tissue and to the conductive mechanism of the pad assembly, while shielding the esophagus with the insulative mechanism of the pad assembly.
 10. The method according to claim 9, wherein the step of transmitting energy comprises transmitting RF energy from the ablation probe of the electrophysiological device through the left atrial wall tissue and to the conductive mechanism of the pad assembly.
 11. The method according to claim 9, wherein the step of transmitting energy through the left atrial wall tissue creates a lesion in the left atrial wall tissue.
 12. The method according to claim 9, wherein the step of transmitting energy through the left atrial wall tissue creates a lesion in a posterior aspect of the left atrial wall tissue. 